Feeding during the rest phase promotes circadian conflict in nuclei that control energy homeostasis and sleep–wake cycle in rats

Food intake during the rest phase promotes circadian desynchrony, which has been associated with metabolic diseases. However, the link between circadian and metabolic alterations is not well understood. To investigate this issue, we explored the circadian of c-Fos immunoreactivity in rats fed during the day, during the night or with free access to food for three weeks. The analysis was focused on the hypothalamic nuclei, which are interconnected and involved in the control of energy homeostasis and/or arousal: the lateral hypothalamic (LH) and perifornical areas (PeF), the arcuate (ARC), ventrolateral preoptic (VLPO) and tuberomammilary nuclei. The results show that food intake during the rest phase flattens the circadian c-Fos expression in the LH and PeF, and induces a phase shift in the VLPO. In addition, c-Fos expression was analyzed in the orexin (ORX) and melanin-concentrating hormone (MCH) neurons of the LH, which are involved in the control of food intake and arousal, and in alpha-melanin stimulating hormone (α-MSH) and neuropeptide Y (NPY) cells in the ARC, all of which are involved in feeding-fasting cycles, energy homeostasis and sending projections to the LH. The results indicate that feeding during the rest phase decreases ORX neurons activation in the light in comparison with the other groups. Feeding during this phase also flattens the activity rhythm of MCH and α-MSH neurons and increases NPY immunoreactivity when the light turns on. This evidence indicates that mealtime affects differentially the hypothalamic nuclei under investigation leading to a circadian conflict that might account for metabolic impairment. This article is protected by copyright. All rights reserved.